AIME is a C++ MUD engine with an OO design, designed to provide utmost flexibility for the designer to create complex worlds. It has a fully-functional builder port, online interpreted specials code, and a flexible levels/quest/profession track system to allow the game owners to set up any world they can imagine.

GNOME-Mud (formerly AMCL) is a Multi-User Dungeon (MUD) client that aims to make mudding a bit easier. It can define aliases, triggers, variables, keyboard shortcuts, and has a connection wizard for easy management of different player characters and MUDs.

Arianne is a multiplayer online engine to develop
turn based and real time games. It provides a
simple way of creating games using Python for a
game's description. Marauroa, its server, uses
Java, MySQL, UDP, and Python for hosting dozens of
players.

AweMUD is a MUD server for use with fantasy-settings. Features include fully dynamic objects and characters, an advanced scripting system, and custom worlds. The engine will eventually have completely interactive rooms (items can be placed under benches, doors can be destroyed), complex magick, and interactive NPCs.

Circle Mud Linux is a three-disk mini-distribution for running the Circle MUD Server. It is based on libc5. It is also a good distribution for MUD players who can use it to quickly and temporarily turn any PC into a MUD console.

CircleMUD is a multi-user dungeon game system (MUD). It is a derivative of DikuMUD Gamma 0.0. A MUD (Multiple User Dimension or Multiple User Dungeon) is a computer program which allows Internet users from around the world to connect to it, create fictional characters for themselves, and then interact with other real users as well as computer-generated entities in a virtual environment.

Crossfire is a multi-player graphical arcade and adventure game made for X. It has certain flavours from other games, especially Gauntlet and the rogue-like games (Nethack, Moria, Angband, and Ragnarok). Any number of players can move around in their own window, finding and using items and battling monsters. They can choose to cooperate or compete in the same world.

Cyphesis is a server for MMORPG games. It is the core engine of the WorldForge project and is currently focused on implementing fantasy games, providing rich scripting, full world persistence, and basic physics.

Dark Lands is a multiplayer RPG made fully with ANSI graphics. The source code is in Pascal. Currently, this game has probably no point except exploring the areas and killing monsters. It can be used as a BBS door game.

DeltaMUD is a MUD server based on enhancements to
the original CircleMUD bpl12 source code and is
thus bound to the legal terms contained within the
CircleMUD and DikuMUD license agreements. The goal
of this project is to provide an enhanced, memory
optimized, and SQL-based version of the original
CircleMUD.